Impact of antiseizure medication taper on electroencephalographic dynamics in focal epilepsy:...

Tapering of the antiseizure medication dosage in the epilepsy monitoring unit can provoke seizures, but its effects on seizure dynamics remain poorly characterized. This study addresses three questions: (1) Does antiseizure medication tapering influence spatiotemporal dynamics of seizures? (2) Does the tapering rate affect these dynamics? (3) Does tapering have a similar effect on interictal epileptic discharges as it does on seizures?

Patients with drug-resistant epilepsy undergoing stereoelectroencephalographic (stereo-EEG) presurgical evaluations at Duke University Medical Center (n = 104) and the Montreal Neurological Institute and Hospital (n = 80) were screened. We included patients in whom the antiseizure medication dosage was tapered from the highest daily dosage (high dosage) to ≤ 50% (low dosage) during stereo-EEG monitoring, and at least one seizure from the same focus was recorded in both conditions. Using an intrapatient design, we compared seizure onset-zone, onset pattern, and propagation dynamics between the two conditions. Given the intrinsic seizure variability, comparisons were made between same-dosage and cross-dosage seizure pairs. We further assessed effects of tapering rates and examined the characteristics of interictal epileptiform discharges.

Among 30 patients, the proportion of channels in the seizure onset zone did not differ between high-dosage and low-dosage conditions (7.25% vs. 8.95%, p = .50, d = -.04). Similarly, no differences were observed in the overlap ratio of seizure-onset regions (62% vs. 64%, p = .72, d = -.01), or the cross-correlation of seizure-onset patterns (.36 vs. .35, p = .54, d = .04) when comparing same-dosage versus cross-dosage seizure pairs. Conversely, seizures at low dosage involved more channels (40.71% vs. 81.49%, p = .001, d = -.39) and lasted longer (33.36 s vs. 74.30 s, p < .01, d = -.47). Tapering rate did not affect seizure dynamics. The mean interictal epileptiform discharge rate and number of propagation channels also remained unchanged.

Despite seizure exacerbation during antiseizure medication tapering, seizure-onset location remained stable. This supports the robustness of seizure-based localization even under reduced medication levels and rapid tapering regimens.